1. Field of the Invention
The present invention relates to an apparatus (hereinafter referred to as “light emitting apparatus”) having an element where a luminescent material is interposed between a pair of electrodes (hereinafter referred to as “luminescent element”). In particular, the present invention relates to a light emitting apparatus (hereinafter referred to as “EL light emitting apparatus”) having a luminescent element (hereinafter referred to as “EL element”) which utilizes a luminescent material (hereinafter referred to as “EL material”) by which EL (electro luminescence) is obtained as the luminescent material. An organic EL display and an organic light emitting diode (OLED: organic light emitting diode) is contained in the light emitting apparatus according to the present invention.
Also, the EL material which can be used in the present invention includes all of the luminescent materials that emit a light (phosphorescence and/or fluorescence) through a singlet excitation, a triplet excitation or both excitations.
2. Description of the Related Art
The EL light emitting apparatus is so structured as to have an EL element with a structure where an EL material is interposed between an anode and a cathode. A voltage is applied between the anode and the cathode to allow a current to flow in the EL material, to thereby re-couple carriers and emit a light. In other words, the EL light emitting apparatus does not require a backlight used in a liquid crystal display device because the light emitting element per se has a light emitting capability. In addition, the EL light emitting apparatus is advantageous in that the apparatus is broad in an angle of visibility and light in weight.
A passive matrix (simple matrix) EL light emitting apparatus is structured in such a manner that a plurality of anodes which are arranged in the form of stripes (bands) in parallel with each other and a plurality of cathodes which are arranged in the form of stripes in parallel with each other are orthogonal to each other, and an EL material is interposed between the anode and the cathode at each of the cross portions. With this structure, a pixel which is at a cross point between a selected (voltage applied) anode and a selected cathode is lit. In other words, a voltage is applied between the anode and the cathode to allow a current to flow in the EL material, to thereby re-couple the carriers and emit a light. The above drive method is called “current drive”.
However, there is a voltage drop (also called “IR drop”) due to a wiring resistance as a phenomenon which is a problem on the EL light emitting apparatus of the current drive type. This is a phenomenon that a voltage drops more as a distance from the power supply becomes farther even if the same wiring is used. This problem is remarkable particularly in the case where the wiring length becomes long, and it is one of obstacles in enlarging a screen of the EL light emitting apparatus.
In particular, in the passive matrix EL light emitting apparatus, a transparent electrically conductive oxide film generally for a visible light is used as the anode, but the electrically conductive oxide film has a problem that the resistance is higher than a metal film, and, thus the conductive oxide film is liable to be influenced by the above-mentioned voltage drop.
There is a fear that the voltage drop caused by the wiring resistance and a signal delay remarkably damage the uniformity of an image quality, cause a residual image phenomenon and become an obstacle to the large screen. The above problems are remarkable particularly in a light emitting apparatus which is several tens inches in a diagonal line.